This invention relates to apparatus and methods for detachably fastening a tool shaft, preferably a drill shaft, in a tool holder. The tool holder is preferably of the type intended for so-called gun drills, and is to be fastened in a drilling machine chuck. Gun drills used for long-hole drilling are provided with a hole passing through the drill for supplying cooling medium under high pressure to the cutting zone.
There has been a need for a tool holder for drills which permits a detachable, secure fastening of the drill. In a previous proposal a round, unprofiled part of the tool shaft, or a profile of the tool shaft evolving into a round part, is to be fastened to a tool holder by means of welding or soldering, as disclosed, for instance, in Canadian Pat. No. 670,003. However, this leads to problems if the drill is to be exchanged without exchanging the tool holder. Therefore, since as a rule, every drill would have to be provided with its own tool holder which involves an unnecessary increase in cost.
According to another publication, viz., U.S. Pat. No. 3,120,768, a profiled drill is to be detachably fastened in a tool holder. An unprofiled part of the drill shaft is soldered to the wall of the tool holder. In order to further assure that the drill does not revolve relative to the tool holder, and in order to prevent leakage of cooling medium between the drill and the tool holder, the outer part of the tool holder is pressed inwardly to bear quite firmly against the profiled part of the drill. In this case exchanging the drill without exchanging the tool holder involves an unnecessarily complicated and expensive procedure.
A third publication, viz., Swedish Pat. No. 226,867, discloses a tool shaft which is detachably fastened to a holder. The drill, which is intended for an easier type of drilling (for instance in dentistry), is fastened in the holder only by means of compressed O-ring gaskets. As a result, this type of drill is quite unsuitable for heavy drilling where great torsional moments are to be transmitted from the holder to the drill shaft. Moreover, a drill with this type of fastening would be unsuitable for instance for long-hole drilling, since the drill shaft would exhibit excessive mobility in the radial direction. This presents significant difficulties in drilling long, straight holes.
An object of the present invention is to eliminate these drawbacks and allow a simple and secure detachable fastening of unprofiled or profiled drill shafts in a tool holder.